This invention relates to a semiconductor test system having a large number of contactors for establishing electrical connection with a semiconductor device under test, and more particularly, to a probe contact system having a planarity adjustment mechanism for adjusting distances between tips of the contactors and surfaces of contact targets such as contact pads of the semiconductor wafer under test.
In testing high density and high speed electrical devices such as LSI and VLSI circuits, a high performance contact structure provided on a probe card must be used. A contact structure is basically formed of a contact substrate having a large number of contactors or probe elements. The contact substrate is mounted on a probe card for testing LSI and VLSI chips, semiconductor wafers, burn-in of semiconductor wafers and dice, testing and burn-in of packaged semiconductor devices, printed circuit boards and the like. The present invention is directed to a probe contact system including such a contact structure.
In the case where semiconductor devices to be tested are in the form of a semiconductor wafer, a semiconductor test system such as an IC tester is usually connected to a substrate handler, such as an automatic wafer prober, to automatically test the semiconductor wafer. Such an example is shown in FIG. 1 in which a semiconductor test system has a test head 100 which is ordinarily in a separate housing and electrically connected to the test system with a bundle of cables 110. The test head 100 and a substrate handler 400 are mechanically as well as electrically connected with one another with the aid of a manipulator 500 which is driven by a motor 510. The semiconductor wafers to be tested are automatically provided to a test position of the test head 100 by the substrate handler 400.
On the test head 100, the semiconductor wafer to be tested is provided with test signals generated by the semiconductor test system. The resultant output signals from the semiconductor wafer under test (IC circuits formed on the semiconductor wafer) are transmitted to the semiconductor test system. In the semiconductor test system, the output signals are compared with expected data to determine whether the IC circuits on the semiconductor wafer function correctly or not.
In FIG. 1, the test head 100 and the substrate handler 400 are connected through an interface component 140 consisting of a performance board 120 (shown in FIG. 2) which is a printed circuit board having electric circuit connections unique to a test head""s electrical footprint, coaxial cables, pogo-pins and connectors. In FIG. 2, the test head 100 includes a large number of printed circuit boards 150 which correspond to the number of test channels (test pins) of the semiconductor test system. Each of the printed circuit boards 150 has a connector 160 to receive a corresponding contact terminal 121 of the performance board 120. A pogo-pi block (test fixture) 130 is mounted on the performance board 120 to accurately determine the contact position relative to the substrate handler 400. The pogo-pin block 130 has a large number of contact pins 141, such as ZIF connectors or pogo-pins, connected to contact terminals 121, through coaxial cables 124.
As shown in FIG. 2, the test head 100 is placed over the substrate handler 400 and mechanically and electrically connected to the substrate handler through the interface component 140. In the substrate handler 400, a semiconductor wafer 300 to be tested is mounted on a chuck 180. In this example, a probe card 170 is provided above the semiconductor wafer 300 to be tested. The probe card 170 has a large number of probe contactors (such as cantilevers or needles) 190 to contact with contact targets such as circuit terminals or contact pads in the IC circuit on the semiconductor wafer 300 under test.
Electrical terminals or contact receptacles (contact pads) of the probe card 170 are electrically connected to the contact pins 141 provided on the pogo-pin block 130. The contact pins 141 are also connected to the contact terminals 121 of the performance board 120 with the coaxial cables 124 where each contact terminal 121 is connected to the printed circuit board 150 of the test head 100. Further, the printed circuit boards 150 are connected to the semiconductor test system through the cable 110 having, for example, several hundreds of inner cables.
Under this arrangement, the probe contactors 190 contact the surface (contact targets) of the semiconductor wafer 300 on the chuck 180 to apply test signals to the semiconductor wafer 300 and receive the resultant output signals from the wafer 300. The resultant output signals from the semiconductor wafer 300 under test are compared with the expected data generated by the semiconductor test system to determine whether the IC circuits on the semiconductor wafer 300 performs properly.
A large number of contactors must be used in this type of semiconductor wafer test, such as from several hundreds to several thousands. In such an arrangement, it is necessary to planarize the tips of the contactors so that all of the contactors contact the contact targets at substantially the same time and with the same pressure. If planarization is not achieved, some contactors establish electrical connections with corresponding contact targets while other contactors fail to establish electrical connections, which makes it impossible to accurately test the semiconductor wafer. To completely connect all of the contactors to the contact targets, the semiconductor wafer must be further pressed against the probe card. However, doing so may physically damage the semiconductor dies due to excessive pressure by contactors.
Furthermore, because of drastic increase in the processing speed of semiconductor chips, contact targets on the semiconductor wafers are becoming more concentrated. Therefore, such testing utilizes a probe card with a large number of probe contactors 190 to contact with contact targets such as circuit terminals or contact pads in the IC circuit on the semiconductor wafer 300 under test. This arrangement requires the probe card and the probe contact system to be able to carry a large number of electrical connections to the test head. Furthermore, because of the small pitch of the contactors, connection from the contactors must be fanned-out to fit to external structures such as a pogo-pin block or an IC package, the probe card needs to be free from physical obstructions.
U.S. Pat. No. 5,861,759 shows an automatic probe card planarization system to planarize a first plane defined by a plurality of contact points of a probe card relative to a second plane defined by a top surface of a semiconductor wafer supported on a prober. A camera is used to measure the height of at least three selected contact points on the probe card relative to the plane of wafer. Based on the measured values, the position of the first plane relative to the second plane is calculated.
With that information and the geometry of the prober and tester, the height variations necessary for the two height variable points are made to planarize the first plane relative to the second plane. This conventional technology requires a camera for visualizing the height of the contact points, resulting in increase in cost and decrease in reliability of the overall system.
U.S. Pat. No. 5,974,662 shows a method of planarizing tips of probe elements of a probe card assembly. The probe elements are mounted directly on a space transformer (contact substrate). It is so configured that the orientation of the space transformer, and thus the orientation of the probe elements, can be adjusted without changing the orientation of the probe card. In this method, an electrically conductive metal plate (virtual wafer) is provided in stead of the target semiconductor wafer as a reference plane. A cable and a computer are also provided in such a way that a computer display shows whether a conductive path is created or not for each probe tip with respect to the metal plate by, for example, white and black dots.
Based on the visual image on the display, the planarity of the probe tips is adjusted by rotating differential screws so that all of the probe tips make substantially simultaneous contact with the metal plate. Because this conventional technology uses a conductive metal plate to establish conductive path for all of probe elements, it requires an extra time to mount the metal plate and replace the same with the target semiconductor wafer. Further, because this method needs a computer and a display to illustrate the states of contact or non-contact of the probe element, an overall cost has to be increased.
U.S. application Ser. No. 09/583,837, which is submitted by the same assignee of the present application shows a planarity adjustment mechanism including a gap sensor for measuring a gap between the contact substrate mounted on a probe card and a target substrate such as a semiconductor wafer at predetermined locations of the contact substrate. The probe card is mounted on a probe card ring formed on a frame of a probe contact system. The planarity adjustment mechanism further includes a rotation adjustment device for adjusting connection members so that the gap between the prove card and the probe card ring is regulated, thereby adjusting the distances between the tips of the contactors and the contact target to be identical to one another.
In this technology, however, since the rotation adjustment device is specially made to engage with the nut of the connection member at the bottom opening thereof, it has a relatively large size. Further, the rotation adjustment device is used on the upper surface of the prove card, it takes up a relatively large space on the prove card. Moreover, the probe card needs to be sufficiently apart from the frame of the system so that the rotational adjustment device can be operated on the probe card without contacting the frame, thereby requiring extra spaces.
Under the circumstances, there is a need in the industry to incorporate a more simple and economical way in a probe contact system to adjust the planarity of the contactors with respect to the surface of the semiconductor wafer.
Therefore, it is an object of the present invention to provide a probe contact system having a planarity adjustment mechanism for adjusting distances between tips of contactors and a surface of a semiconductor device under test.
It is another object of the present invention to provide a probe contact system having a planarity adjustment mechanism and a contact structure mounted on a probe card wherein the contact structure is formed of a contact substrate and a large number of contactors mounted on the contact substrate.
It is a further object of the present invention to provide a probe contact system having a planarity adjustment mechanism for adjusting distances between a contact substrate and a semiconductor wafer under test so that all of contactors on the contact substrate contact the surface of the semiconductor wafer at the same time.
It is a further object of the present invention to provide a probe contact system having a planarity adjustment mechanism for adjusting distances between a contact substrate and a semiconductor wafer under test so that each contactor exerts an identical pressure against the surface of the semiconductor wafer when brought into contact with the semiconductor wafer.
It is a further object of the present invention to provide a probe contact system having a planarity adjustment mechanism for adjusting distances between a contact substrate and a semiconductor wafer under test wherein the adjustment mechanism does not obstruct other components of the substrate handler.
It is a further object of the present invention to provide a probe contact system having a planarity adjustment mechanism for adjusting distances between a contact substrate and a semiconductor wafer under test wherein the probe card has sufficient support and reinforcement to withstand the mechanical pressure during testing.
In the first embodiment of the present invention, a planarity adjustment mechanism is comprised of a contact substrate having a large number of contactors mounted thereon, a probe card for mounting the contact substrate for establishing electrical communication between the contactors and a test head of a semiconductor test system, means for fixedly mounting the contact substrate on the probe card, a stiffener made of rigid material for fixedly mounting and reinforcing the probe card, a probe card ring attached to a frame of the probe contact system for mechanically coupling the probe card to the frame, and a plurality of adjustment members for up/down moving the stiffener relative to the probe card ring at three or more locations on the probe card. Each of the adjustment screws is housed within a through hole formed on the stiffener.
Preferably, the planarity adjustment mechanism further includes flanges on the stiffener each having the through hole for mounting the adjustment member. Each of the three locations of the adjustment members in the through holes of the stiffener corresponds to a vertex of a regular triangle. The adjustment members for moving the probe card are configured by adjustment screws. The through hole on the stiffener has inner threads which engage outer threads of the adjustment screw.
The planarity adjustment mechanism further includes a gap sensor for measuring a gap between the contact substrate and a target substrate at a predetermined location on the contact substrate where the target substrate is a semiconductor wafer to be tested or a reference plate for adjusting the planarity. The gap sensor determines the gap between the contact substrate and the target substrate by measuring capacitance between the gap sensor and an opposing electrode. The reference plate is a metal, ceramic or alumina substrate having electrodes at positions opposite to the gap sensor.
Preferably, the planarity adjustment mechanism further includes a conductive elastomer provided between the contact substrate and the probe card for electrically connecting the contact substrate and the probe card. The planarity adjustment mechanism further includes a support frame provided between the contact substrate and the probe card for supporting the contact substrate and the conductive elastomer through a connection member. The conductive elastomer is comprised of a silicon rubber sheet and metal filaments running in a vertical direction so as to establish communication only in the vertical direction.
In the second embodiment, the planarity adjustment mechanism is comprised of a contact substrate having a large number of contactors mounted thereon, a probe card for mounting the contact substrate for establishing electrical communication between the contactors and a test head of a semiconductor test system, means for fixedly mounting the contact substrate on the probe card, a stiffener made of rigid material for fixedly mounting and reinforcing the probe card, a probe card ring attached to a frame of the probe contact system for mechanically coupling the probe card to the frame, and a plurality of piezoelectric adjustment elements for up/down movements of the stiffener at three or more locations on the probe card in response to electrical signals provided thereto. Each of the piezoelectric adjustment elements is housed within a recess of the stiffener.
In a further aspect, the planarity adjustment mechanism further includes a controller for generating a control signal based on a detection signal from the gap sensor indicating a size of the gap between the contact substrate and the target substrate, wherein the control signal is sent to the piezoelectric adjustment element, thereby automatically controlling the gap between the contact substrate and the target substrate.
According to the present invention, the probe contact system is capable of adjusting the distances between tips of contactors and the surface of the semiconductor wafer under test or the reference plate. The planarity adjustment mechanism is capable of adjusting the distances between the contact substrate and the semiconductor wafer so that all of contactors on the contact substrate contact the surface of the semiconductor wafer at substantially the same time with substantially the same pressure.
The planarity adjustment mechanism for use with the probe contact system incorporates the stiffener to structurally support and strengthen the probe card so that any mechanical pressure applied upon the probe card would not deform or in anyway damage probe card. Furthermore, because the stiffener provided for the planarity adjustment mechanism of the present invention houses the adjustment members such as the adjustment screws or piezoelectric adjustment elements within small ares of the flanges. Thus, it does not physically obstruct the surroundings of the probe card or occupy any area of the probe card. Moreover, the planarity adjustment mechanism of the present invention can be configured as an automatic system by incorporating a controller generating control signals to the piezoelectric adjustment units based on the gaps measured by the gap sensors.